Cleaning metal surfaces to remove grease films

ABSTRACT

A method of treating a wearing surface of a railhead to remove an oil film and improve traction of a locomotive thereon in which effluent from a plasma jet torch is applied to the surface.

[56] References Cited UNITED STATES PATENT 2,787,968 4/1957 Luvisi2,819,681 1/1958 Luvisi 2,890,970 6/1959 Allen 2,906,858 9/1959 Morton,Jr 3,050,616 8/1962 Gage 3,140,380 7/1964 Jensen 3,336,460 8/1967 Haucket 211.. 3,352,997 ll/1967 Butler 3,378,392 4/1968 Longo 2,824,5261/1958 Nohejl Primary Examiner-J. V. Truhe Assislan! Examiner-George A.Montanye Attorney-Townshend & Meserole ABSTRACT: A method of treating awearing surface ofa railhead to remove an oil film and improve tractionof a 1ocom0- tive thereon in which effluent from a plasma jet torch isapplied to the surface.

11 Ill" Illll PATENTEDNBV 16 l97l FIG. 5.

CLEANING METAL SURFACES TO REMOVE GREASE FILMS This application is acontinuation-in-part of my prior U.S.

application Ser. No. 702,864, filed Feb. 5, i968 for Cleaning 5 MetalSurfaces to Remove Grease Films.

This invention relates to a method of treating rails to remove oil filmsand to a method of retarding the establishment of an oil film on atreated rail.

Although in many mechanical devices the provision of an 10 oil filmbetween two coacting surfaces can be advantageous, where a tractiveeffort is to be applied to one of the surfaces then any slip between thetwo surfaces will lead to a loss of efficiency. An example of thisoccurs when considering a railway locomotive tractive wheel and thesurface of the railhead of a railway line. In service the wheel and/orthe surface upon which it runs can become coated with a film of oilwhich will act as a lubricant and permit slipping between the wheel andthe surface. This coating may be only of molecular thickness but it canstill cause substantial loss of tractive effort between the wheel andthe surface. This loss can be appreciable particularly when a locomotiveis accelerating from rest and it has been stated that as much as 1percent of the total mileage covered by a locomotive is travelled underconditions of unsatisfactory wheel/rail adhesion.

Removal of the contaminating film by special chemical and mechanicalmethods has been proposed but this is expensive and capillary and alliedeffects will frequently cause the cleaned surface to be quicklyrecontaminated by the spreading of an oil layer from adjacent uncleanedparts of the metal surface.

Recent research in rail adhesion implicates boundary lubricationphenomena as one reason for a low value of wheel/rail adhesion. Thesephenomena cause the metal surface to actually react with the surfacecontaminants forming tenacious and strongly adhering films.

According to the invention there is disclosed a method of treating awearing surface of a railhead to improve traction of a locomotivethereon by removing an oil film from the wearing surface comprisesdirecting a gaseous effluent from a plasma jet torch onto the surface,the exposure to the effluent being short enough to have no deleteriouseffect on the railhead.

The method of the invention is to be distinguished from prior artmethods of cleaning a rail to dry the rail and to remove oil films inwhich an intense flame from a suitable chemical burner is applied to therailhead. The action of the flame is to heat a portion of the railheadand when the temperature of this has reached a sufficiently high valuethe thin oil film is burned off. This method necessitates the raising ofthe temperature of the rail into the region where an adverse effect onthe original heat treatment of the rail will be caused. In additionsince the rail acts as a heat sink only a small proportion of theapplied heat will actually have any action on the oil film. Thisinherent inefficiency of the thermal method of destroying the film willcause the cost of using the method to rise sharply if it is required foroperation on a locomotive that is running at 5 or 10 mph. The cost ofproviding any significant thermal heating of the railhead when runningat 50 mph. may well prove more objectionable than the original lossesdue to wheel slippage.

Although hitherto the plasma jet torch has been used as a source ofintense heat in welding and cutting operations, it is not this propertyof the torch which plays a significant part in the present invention.The plasma torch can also act as a rich source of ions and free radicalsand other highly reactive substances and these can be carried in afast-moving gaseous stream to the railhead where they will have aneffect directly on the oil film contaminating the metal surface withoutthe need to transfer a substantial amount of thermal energy into thissurface to cause an appreciable rise in its temperature.

The chemical reactions leading to the destruction of the thin filmcontaminating the railhead takes place instantaneously and the kineticenergy of the plasma jet helps to remove the reaction products.producing in the railhead surface a state of considerably increasedfrictional properties.

LII

In order to establish beyond any doubt that the method used in thepresent invention does not rely on thermal decomposition of the surfacecontaminants the following experiment was performed:

A plasma torch operating in a nontransferred mode and dissipating 25 kW.was suspended 8 cm. above a standard oil contaminated rail. After alO-seconds-burst of a stationary plasma jet the surface temperature ofthe rail was measured by means of a precision surface temperature gaugeand was found to be 82 C., while the body temperature of the rail,measured at a depth of 1 cm. below the surface, directly below theimpinging plasma jet was found to be 61 C. These very low figuresindicate that the decomposition of the oils and greases present on thesurfaces of the rail could not have been accomplished by pyrolysis orany other form of thermal decomposition.

This point was further proved by exposing the same rail to a flame of atown gas torch, for a sufficiently long time to allow the surfacetemperature of the rail to rise to 280 C. Even at that temperature thecontaminants were not decomposed and on subsequent measurement with atribometer a low value of friction was obtained.

The plasma jet torch for treating the rail may conveniently be carriedon the locomotive in a suitable position enabling it to be directed onto the rail surface. The torch might alternatively be positioned so asto treat a tractive wheel of the vehicle or possibly to treat both awheel and the rail. The apparatus may be positioned on the locomotive soas to treat the rail ahead of the main direction of movement of thelocomotive. The plasma jet may be also used to carry catalysts to therail to promote the breakdown of the oil film. in addition to catalystsit is also within the scope of the invention to introduce into theplasma jet small quantities of substances or precursors of substanceswhich will inhibit recontamination. Methods of providing such additiveswill be disclosed later in this specification.

An additional disadvantage of the former chemical and mechanical methodsof cleaning a rail that have already been discussed is that a freshlycleaned area of the metal surface can become quickly recontaminated by afurther oil film which spreads over the cleaned surface from adjacentuncleaned parts of the metal. it will be clear that even if the uppersurface of the railhead has been thoroughly cleaned there will bequantities of oil on the sides of the rail that cannot be reached and ina matter of only minutes this will spread over the cleaned surface againso that the original condition is reestablished. The temporary cleaningeffect that was produced by these former methods may thus be adequatefor a single locomotive to pass over a given stretch of railway line butthe tractive conditions will probably deteriorate considerably within ashort time.

The present invention also comprises a method of retarding therecontamination of a cleaned area of the rail surface. Suitableinhibiting agents may be brought into contact with the treated surface,the agents acting to slow down the advancement of the oil filmtherealong so that the effect of the cleaning treatment will beprolonged. Conveniently the plasma jet torch may be used to convey theinhibiting agents to the metal surface. Examples of suitable inhibitingagents are given later in this specification.

By way of example, embodiments of the invention will be described withreference to the accompanying drawings in which,

FIG. 1 shows a tractive wheel of a locomotive on a rail,

HO. 2, is a cross section through the line ll-ll on FIG. 1,

FIG. 3 is an enlarged cross section through the line ill-lll on FIG. 2,

FIG. 4 shows a tractive wheel of a locomotive with ad jacently mountedplasma nozzle, and,

FIG. 5 shows a tractive wheel of a locomotive with plasma nozzledirected between the wheel and a rail.

When a tire I of a tractive wheel of a railway locomotive 1A is incontact with a rail 2 the actual area of contact is generally in theshape of an ellipse, 3. It has been shown that ifa tractive effort isapplied to a wheel which is allowed to roll in the direction 4, aforward part 5 of the contact area of both bodies will remain rigidlytogether, while a rearward part 6 will experience relative slipping. Adividing line between the two parts will not be clearly defined but anincrease in the tractive effort applied will result in an increase ofthe slipping rearward part of the area and the nonslipping forward areawill be reduced. The forward area will eventually disappear and slippingofthe wheel will take place.

The presence of contaminants on the coacting surfaces will generallycause a reduction of the adhesion between them. With a plasma jet nozzle7, mounted ahead of the tire I a portion of the rail 2 can be passedthrough the jet before the rail comes into contact with the wheel. Theplasma jet of elongated cross-sectional area which in operation issuesfrom the jet is positioned so that its major axis is at right angles toa longitudinal axis of the rail. in this position, the shape of the jetas it impinges on the rail can be substantially the same as that of theellipse 3. The combination of radiations from the jet, which as is wellknown to those skilled in the art, will produce further ionizedparticles, free radicals, and other highly reactive substances, andpossibly also of the high kinetic energy of the jet stream have beenfound to have an adhesion increasing effect on the rail surface and toincrease adhesion between the rail and the tractive wheel tire 1.

In a further example a plasma jet nozzle 7 as shown in FIG. 5 wasmounted between the rail and wheel tire close to the point where thesecome into contact. The plasma jet is thus enabled to treatsimultaneously the rail and tire surfaces.

A series of experiments was carried out using the plasma jet apparatusand details of the results obtained are given below:

A standard railway rail 5 yards in length was mounted horizontally and aplasma jet nozzle assembly carried on a tractor was positioned formovement directly above the rail. The distance between the nozzle andthe upper surface of the railhead was made adjustable and could bevaried between half an inch and 8 inches.

The rail was lightly wiped with an oiled cloth until its coefficient offriction fell from a value of 0.53 to 0.12. The tractor was started andthe plasma nozzle assembly made to travel along the rail at speedsranging from 0.1 to 20 mph.

ln a series of tests the nozzle was operated in a nontransferred arcmode. As shielding gas, mixtures of nitrogen and argon were used inratios from 10:3 to 1:1 respectively. The volumes of total gas usedvaried with power consumption from 25 c.f.h. and 8 kw. to 150 c.f.h. and24 kw.

The experiments were conducted using nozzles providing jets of circularand of elliptical cross section. The circular nozzles affected a zone of3 cm. in width on the railhead when at a height of 5 inches above therail. The nozzle providing an e1- liptical jet affected the whole flatportion of the rail that is about 5 cm. in width at the height of5inches.

After carrying out one pass with the plasma jet the coefficient offriction of the rail was measured immediately after the treatment andwas found to be of about 0.5 or higher. This high value of friction wasretained for approximately 5 or 10 minutes without change, and then itsvalue started to drop progressively, reaching 0.35 within 2 to 4 hours.

Additional mechanical cleaning of the rail was also tried by jettingfinely powdered silica through the plasma jet at rates of from 0.1 to 12g. per minute. It was found that the coefficient of friction wasrestored and remained restored for substantially longer periods whichvaried from 10 to hours in laboratory conditions.

Good results were also obtained when fine aqueous col-' loidalsuspensions of silica were introduced to the plasma jet or alternativelywhen alkali or alkaline earth metal silicates were introduced throughthe plasma jet. The best results in this series of experiments wereobtained with 1 percent w./v. aqueous solutions of potassium silicatewhich was introduced through the plasma jet at a rate of approximately 2ml./min.

The above methods increased the time during which the plasma-treated oilcontaminated surface of the rail retained its lgh frictional properties.A further increase In the frictional properties of the contaminatedsurfaces were obtained by depositing electrolytically or chemicallylayers of nickel, cobalt, rhodium and rhenium or alloys thereof in thearc-constricting passages of the plasma torch and also in the immediatevicinity of the arc exit, in the region known as the arc root zone andalso in the arc chamber itself. These deposits, as was confirmed byspectroscopic measurements, are slowly ablated in the environment of thearc evolving their respective vapors in the region surrounding theplasma jet. It was found that the use of such layers increasedfrictional properties of the railhead surfaces even at substantiallyhigh velocities of plasma traverse, without the need of increasing theelectrical power supplied to the plasma torch.

The foregoing descriptions of embodiments of the invention have beengiven by way of example only and a number of modifications may be madewithout departing from the scope of the invention. For instance, thestream of effluent emerging from the jet nozzle may contain additionalor alternative gases to those specifically described. Ingredients suchas water might be added to the jet to modify the effects of the plasmaeffiuent.

Use of the apparatus of the invention has been found to be particularlysuitable on a railway locomotive of comparatively light weight such as adiesel-electric, electric or pneumatic locomotive. The reduction ingross weight of the locomotive can thus be effected without any tendencyfor increased slippage of the tractive wheels to occur.

lclaim:

l. A method of treating a wearing surface of a railhead to improvetraction of a locomotive thereon by removing an oil film from thewearing surface, comprising the step of directing an effluent from aplasma jet torch onto the wearingsurface, the exposure to the effluentbeing sufficiently short in duration to have no deleterious effect onthe wearing surface and to cause no appreciable rise in the temperatureof said wearing surface, the destruction of the oil film being theresult of a substantially instantaneous reaction between theconstituents of said plasma and the oil film at a nonpyrolytictemperature for said oil film, and the removal of the products of saidreaction from the wearing surface being effected by the kinetic energyof the plasma jet.

2. A method according to claim 1, in which a nozzle of the plasma torchis electrically connected for operation in a nontransferred arc mode.

3. A method according to claim 1, in which the plasma jet torch isdirected into a space between the railhead and a locomotive wheel.

4. A method according to claim 1, in which silicon compounds are fedinto the plasma torch for delivery to the surface.

5. A method according to claim 4, in which the silicon compound issilica.

6. A method according to claim 4, in which the silicon compound ispotassium silicate.

7. A method according to claim 1, in which a catalyst selected from thegroup consisting of nickel, cobalt, rhodium, rhenium and alloys thereofis fed into the plasma torch for delivery to the surface.

8. A method according to claim 7, in which the catalysts are derived byablation of a constricting member of the plasma torch.

2. A method according to claim 1, in which a nozzle of the plasma torchis electrically connected for operation in a nontransferred arc mode. 3.A method according to claim 1, in which the plasma jet torch is directedinto a space between the railhead and a locomotive wheel.
 4. A methodaccording to claim 1, in which silicon compounds are fed into the plasmatorch for delivery to the surface.
 5. A method according to claim 4, inwhich the silicon compound is silica.
 6. A method according to claim 4,in which the silicon compound is potassium silicate.
 7. A methodaccording to claim 1, in which a catalyst selected from the groupconsisting of nickel, cobalt, rhodium, rhenium and alloys thereof is fedinto the plasma torch for delivery to the surface.
 8. A method accordingto claim 7, in which the catalysts are derived by ablation of aconstricting member of the plasma torch.